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https://issues.apache.org/jira/browse/SOLR-13257?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16900547#comment-16900547
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Michael Gibney commented on SOLR-13257:
---------------------------------------
Thanks [~tomasflobbe] and [~cpoerschke] for your feedback, and for helping move
this feature along! I just pushed some commits to address some points raised by
[~cpoerschke]: opting for stricter handling of the {{dividend}} param (if
present, it must be an integer), and adding/clarifying documentation and
javadocs.
Most of the changes have to do with added documentation. One functional change
was to add support for the ability to explicitly disable implicit hash-based
routing (by setting the {{hash}} param config to the empty String, in
solr.xml). This idea came up as a consequence of thinking about edge cases
while documenting the behavior of replica routing configuration in solr.xml.
> Enable replica routing affinity for better cache usage
> ------------------------------------------------------
>
> Key: SOLR-13257
> URL: https://issues.apache.org/jira/browse/SOLR-13257
> Project: Solr
> Issue Type: New Feature
> Components: SolrCloud
> Reporter: Michael Gibney
> Assignee: Tomás Fernández Löbbe
> Priority: Minor
> Attachments: AffinityShardHandlerFactory.java, SOLR-13257.patch,
> SOLR-13257.patch
>
> Time Spent: 3h 40m
> Remaining Estimate: 0h
>
> For each shard in a distributed request, Solr currently routes each request
> randomly via
> [ShufflingReplicaListTransformer|https://github.com/apache/lucene-solr/blob/master/solr/core/src/java/org/apache/solr/handler/component/ShufflingReplicaListTransformer.java]
> to a particular replica. In setups with replication factor >1, this normally
> results in a situation where subsequent requests (which one would hope/expect
> to leverage cached results from previous related requests) end up getting
> routed to a replica that hasn't seen any related requests.
> The problem can be replicated by issuing a relatively expensive query (maybe
> containing common terms?). The first request initializes the
> {{queryResultCache}} on the consulted replicas. If replication factor >1 and
> there are a sufficient number of shards, subsequent requests will likely be
> routed to at least one replica that _hasn't_ seen the query before. The
> replicas with uninitialized caches become a bottleneck, and from the client's
> perspective, many subsequent requests appear not to benefit from caching at
> all.
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